The present invention relates to a semiconductor device and more particularly to a semiconductor device with a polycrystalline silicon (hereinafter referred to as poly-Si) resistor having a resistance within a predetermined range.
A resistor employed in a semiconductor integrated circuit device is generally formed in an isolation region for the purpose of reducing parasitic capacitance and for high integration of the device. In the past such resistors have been commonly formed using a poly-Si film, and either have a low resistance as low as several k.OMEGA. or less or a very high resistance as high as several tens G.OMEGA. or more. Examples of such resistors are discussed in Solid. State Electronics, Vol. 20 (1977), pp. 883-889, and in Technical Digest of IEDM (1986), pp. 300-303.
Meanwhile, a resistor for SRAM (Static Random Access Memory) is required to have a resistance of about 40 k.OMEGA.-800 k.OMEGA.. In this case, there are several problems to form the resistor having a resistance of 40 k.OMEGA.-800 k.OMEGA. using the poly-Si film since as mentioned above, the resistor using the poly-Si film has either a low resistance of several k.OMEGA.'s or a very high resistance.
More specifically, in order to form the resistor having a resistance of 40 k.OMEGA.-800 k.OMEGA. using the poly-Si film, required are conditions that (1) the process for forming a resistor is so stable as to provide a desired resistance with a high accuracy, (2) the area required for a resistor is small and (3) the completed resistor has a sufficiently high reliability.